The present invention relates to a simple method of measuring the weight of nitrogen oxide emitted from an engine of a vehicle such as a motorcar running on an actual road surface.
As is well-known, nitrogen oxide (hereinafter referred, to as xe2x80x9cNOxxe2x80x9d) is one of the components determined as an air pollutant among gases (hereinafter referred to as xe2x80x9cexhaust gasxe2x80x9d) emitted from an engine of a vehicle, e.g., motorcar. The concentration of NOx contained in the exhaust gas from the engine is greatest when operating in a city in terms of speed and load and is lower in other areas. It is therefore necessary to apply a moderate load to a motorcar when measuring the NOx emission.
In view of this, conventionally a motorcar is mounted on a chassis dynamometer, and allowed to run in accordance with a predetermined running pattern. The speed; torque and the like of the engine are regulated to apply a proper load to the motorcar, and a NOx analyzer, such as a chemiluminescent detector (CLD) is used to measure NOx contained in the exhaust gas.
However, in the aforementioned conventional technique, considerably large-scale equipment such as a chassis dynamometer is required in addition to a NOx analyzer. Facilities required for measurement increase measurement costs. The measurement of NOx using the chassis dynamometer unit is primarily conducted to measure NOx of motorcars, e.g., new cars, which have not yet been run. Motorcars which have been put to use, namely, the so-called used cars are usually not subjected to measurement using the chassis dynamometer unit. It is to be noted that the used car is measured in a fact-finding survey but its proportion is relatively low.
As aforementioned, to measure the concentration and weight of NOx emitted from a motorcar, the measurement is preferably made in such a condition that a proper running load is applied to the motorcar.
Meanwhile, applicant has applied a patent entitled xe2x80x9cSimple Method Of Measuring Nitrogen Oxide In Running Vehiclesxe2x80x9d on Jan. 29, 1999 as a technique for simply measuring the weight of NOx emitted from an engine when a vehicle, e.g., motorcar, is allowed to run on an actual road surface (JP-A-11-23016). The method of measuring the weight of NOx according to this patent application has a system in which the flow rate of exhaust gas is determined using an intake air flow meter or an exhaust gas flow meter while measuring the concentration of NOx using a NOx analyzer to determine the weight of NOx emitted from an engine on the basis of the above NOx concentration and flow rate of exhaust gas in a simple manner.
However, since the flow rate of exhaust gas is determined using an intake air flow meter or an exhaust gas flow meter in the method of measuring the weight of NOx in the aforementioned patent application, the flow meter must be calibrated to determine the flow measurement. Also, pressure drop affords possibility for producing errors in the values measured of the exhaust gas flow rate and the point in question is open to further improvement.
The present invention has been conducted taking the above situation into consideration and one of the objects is to provide a simple method of measuring NOx in a running vehicle (hereinafter simply referred to as xe2x80x9cNOx simple measurement methodxe2x80x9d). The method ensures that the weight of NOx emitted from the engine, while running the vehicle on an actual road surface, can be determined more simply and accurately.
The above object is attained by a NOx simple measurement method in accordance with the present invention. The method comprises mounting a NOx analyzer, an air-fuel ratio sensor, and a data collection device on a vehicle, allowing, the vehicle to run on an actual road surface, introducing the exhaust gas emitted from an engine to the NOx analyzer in order to determine the concentration of NOx contained in the exhaust gas, determining the flow rate of the exhaust gas by using the fuel injection quantity based on the fuel injection pulse output from an electronic control unit mounted on the vehicle and the output of the air-fuel ratio sensor, and determining the weight of NOx emitted from the engine from the flow rate of the exhaust gas and the concentration of NOx.
In the NOx simple measurement method of the present invention, a vehicle is allowed to run on an actual road surface at varying speeds and gear ratios to thereby apply a proper load to the vehicle, and NOx is generated under the load. The concentration of NOx is then measured by a NOx analyzer mounted on the vehicle. On the other hand, the flow rate of the exhaust gas is found using the fuel injection quantity based on the fuel injection pulse output from an electronic control unit mounted on the vehicle and the output of the air-fuel ratio sensor. Accordingly, a given calculation is made using the flow rate of the exhaust gas and the concentration of NOx wherein the weight of NOx emitted from an engine can be found. Thus, the weight of NOx generated from an engine running on an actual road surface can be measured in real time.
When a direct insertion type NOx analyzer is used as the aforementioned NOx analyzer and is attached to an exhaust pipe connected to an engine, the structure of a measurement system is made simple.